The present invention relates to a sheet supplying apparatus for sequentially separating a sheet stacked on a stacker and supplying the sheet to a processing platen, so that an image on the sheet is read at the processing platen or the sheet is printed, and also relates to an image reading apparatus such as a copier or a scanning device comprising the sheet supplying apparatus.
In general, a sheet supplying apparatus sequentially separates and delivers a sheet stacked on a sheet feeding stacker to a processing platen such as an image reading platen or a printing platen for processing, and discharges the processed sheet to a sheet discharging stacker. The sheet supplying apparatus is also used as a scanner device for reading an image or as a document feeding apparatus of a copier.
In a conventional sheet supplying apparatus such as a scanner apparatus or a copying apparatus, in many cases, a sheet feeding stacker and a sheet discharging stacker are arranged in a vertical direction in order to reduce an installation space of the apparatus. Sheets such as original documents are supplied from the sheet feeding stacker to the sheet discharging stacker via a U-shape conveying path.
To reduce the size of the apparatus with such a configuration, it is necessary to reduce a distance between the sheet feeding stacker and the sheet discharging stacker, thereby reducing a height and a width of the apparatus. Accordingly, in the height direction of the apparatus, the U-shaped path needs to have a large curvature, thereby feeding a sheet in a curved shape. In the width direction of the apparatus, it is necessary to reduce a size of a driving motor and a transmitting mechanism disposed an outside of a width of a sheet.
While it has been desired to reduce the size and weight of the apparatus, the apparatus needs to handle sheets having various sizes and thicknesses, and made of various materials such as paper and a plastic film. Conventionally, a normal office sheet has a weight between 45 and 180 gm2. For the desk top printing (DPT), a cardboard having at least a weight of 200 gm2 has been recently used, for example, for a front cover. When an apparatus designed for handling sheets having a weight from 45 to 180 gm2 was used for feeding a sheet having a weight of 200 gm2, it was found that the sheet was caught in a U-shaped path and a driving motor was locked, thereby preventing smooth transport. Further, the sheet slipped while moving to a processing platen.
The problem may be caused by friction between the sheet and a transport path extending from the sheet feeding stacker to the sheet discharging stacker. To solve this problem, it is necessary to use a driving motor with high driving power, thereby increasing the size of the apparatus.
Japanese Patent Publication (Kokai) No. 2003-81474 has disclosed a structure in which an idle roller is disposed in the U-shaped path at an upstream side of a processing platen for reducing friction between a sheet and a conveyance guide. Japanese Patent Publication (Kokai) No. 2843492 has disclosed a structure in which idle rollers are arranged in front of and behind a processing platen (image reading platen), respectively, for preventing the processing platen from disturbing a sheet. In the disclosed structure, the idle rollers are placed near the processing platen (image reading platen) and at a central portion of the U-shape conveying path.
However, even if such an idle roller is disposed at a substantially central portion of the U-shaped path for reducing friction, when a distance between a sheet feeding stacker and a discharging stacker is reduced, a sheet receives a large resistance at an outlet of the sheet feeding stacker and an inlet of the sheet discharging stacker, thereby making it difficult to transport the sheet smoothly. When a length of the U-shaped path is reduced, a leading end of the sheet receives a large frictional resistance at a conveyance guide near the discharging stacker and a trailing end of the sheet receives a large frictional resistance at a conveyance guide neat the sheet feeding stacker. Accordingly, even if the idle roller is disposed at a substantially central portion of the U-shaped path, it is difficult to reduce the friction. As a result, with the conventional structures disclosed in the patent references described above, it is difficult to accurately feed a wide range of sheets from thin paper to cardboard. It is also difficult to effectively reduce the size and weight of the apparatus.
Further, in the conventional structures described above, it is difficult to prevent disturbance of a sheet when a leading end thereof enters the processing platen and prevent flip-up of a sheet when a trailing end of the sheet moves away from a sheet feeding roller. In the structure disclosed in Japanese Patent Publication (Kokai) No. 2843492, the idle roller is disposed between the sheet feeding roller and the processing platen. However, in the structure, the sheet feeding roller is provided far away from the processing platen, and the idle roller is simply provided between the processing platen and the sheet feeding roller for reducing the frictional force.
In view of the problems described above, an object of the present invention is to provide a sheet supplying apparatus having a U-shaped path extending from a sheet feeding stacker to a sheet discharging stacker in which a load between a sheet and a guide constituting the path is reduced. It is also an object of the present invention to provide a sheet supplying apparatus with a reduced size and weight for accurately supplying a sheet to a processing plate for reading an image or the like at a stable speed.
Another object of the present invention is to provide a sheet supplying apparatus in which a leading end and trailing end of the sheet are stably guided from a sheet feeding roller to a processing platen, thereby preventing disturbance of the sheet when the leading end of the sheet enters the processing platen and flip-up of the sheet when the trailing end of the sheet moves away from the sheet feeding roller. It is also an object of the present invention to provide a sheet supplying apparatus in which the sheet does not float from the processing platen or is not disturbed by a shock when the sheet is transported downwardly from the processing platen. It is also an object of the present invention to provide an image reading apparatus using the sheet supplying apparatus.
Further objects and advantages of the invention will be apparent from the following description of the invention.